The present disclosure relates to a pump system, and more particularly, to a pump system and a method for operating the pump system that are designed to prevent unnecessary energy consumption caused by a no-load operation of a motor by putting the motor into sleep mode when the pump is in no-load operation in a no-flow state.
In an application field where mainly flow rate and hydraulic pressure are controlled with a fan or a pump, a multiplicity of electric motors are used to control flow rate, hydraulic pressure, air flow, or wind pressure. In general, there are a few specific requirements for electric motors used in the heating, ventilating, and air conditioning (HVAC) market to meet surrounding conditions, e.g., building communication protocols. Also, technology to deal with a situation where an electric motor is laid in a wet environment may be included in an inverter functioning as a controller. From an end user's perspective, it means the single controller conducts self-adjustment in all situations to minimize energy consumption. In addition, it may lead to a reduced total cost of ownership (TOC) for the same entire system and a reduced facility cost.
In the case of an alternating current (AC) motor driving system of the related art, the power of a commercial power source is varied in voltage and frequency and is then supplied to AC motor. Therefore, an AC motor driving system is a variable speed motor driving system in which motor speed and torque can be easily controlled with high efficiency. In such AC motor driving system, a single inverter controller may be used to control a multiplicity of electric motors mainly for adjusting the flow rate and hydraulic pressure of a fan or a pump.
In general, a controller such as an inverter controls a single main motor on a proportional-integral-derivative (PID) basis by using a built-in PID controller according to process control variables received by feedback. If necessary, an auxiliary motor may be adopted, and an external signal may be controlled for common operation and feedback control variables may be maintained constantly.
During operation control based on multi-motor control (MMC), an auxiliary motor is turned on or off automatically when a preset flow rate or hydraulic pressure is so insufficient or excessive that control by only a main motor alone is impossible. In this case, the merit is that a user can save energy by using the controller. The economical operation mentioned before may be set up by using sleep and wake modes if the load amount is small.
A controller considers the followings as a sleep mode in a pump system of the related art:
1) For operation frequency to be at or below sleep frequency satisfying a sleep condition
2) For all multi-controlled auxiliary motors of an inverter to remain halted
3) For a main feedback level to be lower than a preset level
4) Lapse of time equal to or longer than a stable system delay time set by a user
In the related art, normal sleep and wake-up operations can result in energy saving if all of the abovementioned conditions are satisfied. When a controller determines that a control variable required under a load is sufficient, the controller suspends output and an inverter stops a system. In this case, if a load amount increases again with time, the controller operates the inverter for operation suitable for the load by checking a load detection sensor.
FIG. 1 is a diagram illustrating the abovementioned sleep mode operation and wake operation sequence.
Referring to FIG. 1, the sleep and wake-up operations are conducted in the aforementioned manner in most loads currently applied. However, when actual frequency does not reach sleep frequency due to pump characteristics despite a small load amount, sleep mode conversion is not made even when the load amount is small.